1. Field of the Invention
The present invention relates to fiber optic transmission of signals through a manifold or data bus. More particularly, the present invention relates to the use of a single-optical-fiber transmission line coupled with a low-loss launch coupler to provide the data link for information transmission to and from the master terminal and with a series of slave terminals, each capable of receiving bidirectional signals carried in the transmission line and each capable of sending signals through the transmission line in a single direction.
2. Description of the Prior Art
Fiber optic devices, once a laboratory curiosity, are now receiving considerable attention and are used in industry. Fiber optic communication cables for telephone systems are not in limited service and conversion to "Lightwave Communications Systems" has been predicted for many telephone utilities.
Uses such as those noted above often require multiple connections for signal reception and use, since a large number of terminals are provided. The interconnection means is commonly described as a data bus. Data buses are used in the electronics industry to provide communication links between isolated terminals in applications such as computer systems, airplane and ship controls, electronic test equipment and weapons control systems. It has become generally known that wire transmission lines are of limited utility in many of the above uses due to such factors as limitations in bandwidth to the extent that the transmission line capability is substantially lower than the data production capability of the equipment. In addition, wire transmission lines are susceptible to electromagnetic interference from external sources and transmit only in a given direction at a given time. Thus the only means for utilizing wire transmission in a bidirectional manner is multiplexing of the signals that are transmitted. Fiber optics, on the other hand, has the potential capability of elimination of these problems, since fiber optic units are capable of transmission in a bidirectional mode and are immune to electromagnetic interference.
d'Auria et al in U.S. Pat. No. 3,953,727 suggests a system for single-optical-fiber transmission utilizing mirrors, photodetectors and diodes to generate signals for and receive signals carried in a fiber optic line.
Chown et al in U.S. Pat. No. 4,166,946 and Kogelnik in U.S. Pat. No. 3,986,020 both suggest optical fiber transmission systems. Chown et al uses a bundle of multiple fibers and utilizes couplings to connect the fibers to the terminals and remove portions of the signal from the main transmission line. Kogelnik, on the other hand, uses a strip guide or fiber and laser signals to pick off signals from plural stations and selectively transmit them to remote stations.
In another system, Suzaki in U.S. Pat. No. 4,136,929 utilizes a closed loop which receives its signal by tapping off a portion of the signal contained in an external transmission line. The closed loop utilizes the signal and returns the remaining signal to the transmission line at the point of take-off.
In U.S. Pat. No. 4,089,584 of Polczynski a manifold concept utilizing an arbitrary number of terminals is disclosed. The structure of the optical couplers and the means of fabrication are not provided. Only one terminal transmits to the other terminals at a given time and the signal flow is unidirectional. A bus using such a manifold is half duplex and the data is time-division-multiplexed.